A trade-off between root growth response and proline hyper-accumulation in plants exposed to heavy metals

Proline hyper-accumulation is one of the widely reported responses of plants exposed to heavy metals. The present study observed the level of proline hyper-accumulation in 20 crop plants exposed to Cu and in T. aestivum exposed to various heavy metals. Differential observations in resistance (growth as indicator), avoidance (of Cu/ heavy metal) and tolerance (proline hyper-accumulation as indicator) of these plants to heavy metals was studied. Avoidance and tolerance were not correlated and found to be independent of total Cu accumulation. In 75% plant tolerance was correlated negatively with root growth (or positively with root growth inhibition). These results indicate a trade-off between root growth and proline hyper-accumulation (tolerance) to Cu stress. Crops with higher proline accumulation (tolerance) showed less root growth.